1. Field of the Invention
The present invention relates to an excitation atomic beam source, in particular to a high-velocity excitation atomic beam source for use in doping impurities into a semiconductor material in a thin film process and the like.
2. Description of the Prior Art
Below described are conventional excitation atomic beam sources with reference to FIGS. 6 and 7.
FIG. 6 shows a conventional excitation atomic beam source, for example, the "Radical Beam Source" made by Oxford Applied Research. The excitation atomic beam source is provided with a plasma generation chamber 61 whose peripheral wall is made of glass. High-frequency coils 62 are wound around the chamber wall. When nitrogen gas is fed into the plasma generation chamber 61 through a gas inlet tube 63, a high-frequency plasma 64 is produced in the chamber 61 upon application of high-frequency waves from the coils 62. Excited nitrogen atomic beams together with electrons, ions, and neutral particles are generated in the plasma 64 and emitted into a process chamber 66 through a hole 67 defined in a beam outlet plate 65 due to a pressure difference.
However, in such an excitation atomic beam source, excited atoms emitted through the hole of the plate 65 are diffused to reach a workpiece in the process chamber 66, and therefore it would be difficult to obtain sufficient nitrogen doses required to produce, for example, a p-type ZnSe semiconductor device or the like device.
FIG. 7 shows another type of a conventional high-velocity atomic beam source as disclosed in the Japanese Patent Unexamined Laid Open Hei 1-313897, where an electric discharge takes place in a gap between a needle-shaped anode 71 and an ion-neutralizing nozzle 73 protruded from a first cathode 72 to thereby generate a glow discharge in the space by a high d.c. voltage application. A magnetic field is applied to the gap between the anode 71 and the nozzle 73 by a magnet 77. A gas is supplied to the nozzle 73 through a gas inlet tube 76 to be dispersed in a space between the anode 71 and the cathode 72 so that ions are contacted with the gas. Ions produced by the glow discharge are converged to have high density and accelerated by an applied electric field toward the nozzle 73 and fed back into the nozzle 73. When the ions are contacted with the gas remaining in the nozzle, each ion loses its electric charge and turns to a neutral atom. In this case, kinetic energy of the ions is taken up by the neutral atoms to form a high-velocity atomic beam in the nozzle 73, which the resultant atomic beam is emitted outside from the nozzle 73.
According to the construction mentioned above, the high-velocity atomic beam emitted through the nozzle 73 is converged to have a high convergent quality approximately equal to the inner diameter of the nozzle.
In this type of the conventional construction, however, the anode and cathode, which function as high d.c. voltage electrodes, are used for generating a glow discharge. Therefore, a mixture of impurities due to use of the anode and cathode can not be avoided, and it is impossible to reduce a processing gas pressure.
Moreover, an atomic beam is excited in the glow discharge space before the nozzle and then the excited beam is derived through the nozzle to the outside. Therefore, it is difficult to obtain high excitation and high-density doses of atomic beams with low power and low gas pressure.
As described above, in the conventional atomic beam source, there has not been suggested or taught any excitation atomic beam source in which a plasma is generated in a space between a nozzle and a skimmer using a microwave for exciting a processing gas.